The present invention relates to artificial implant devices adapted to be implanted in blood-contacting position in the bodies of living creatures such as human beings, and, more particularly, to the flocking of the blood-contacting surfaces of such devices to promote the formation of stable and viable biological linings on such surfaces.
In recent years, concentrated efforts have been made toward the development of various artificial implant devices for implantation in blood-contacting position in the human body, such as artificial heart devices and various blood circulatory assist devices. One of the problems encountered in connection with such long-term prosthetic devices is ensuring that the blood-contacting surfaces of such devices are sufficiently blood-compatible so as not to cause thrombosis, destruction of the formed elements in the blood, alteration of the plasma proteins, destruction of enzymes, depletion of electrolytes, adverse immune responses, damage to adjacent tissue, cancer, or toxic or allergic reactions. One approach to this problem has been the use of textured surfaces which will initiate deposition of fibrin from the blood to promote the formation of a stable and viable biological lining and which will provide secure anchoring for such lining. It has previously been proposed to form such textured surface by flocking the blood-contacting surfaces of such artificial implant devices with fibers of a blood-compatible polymeric material, such as polyester or nylon. In accordance with such proposal, the blood-contacting surface is first coated with a layer of suitable adhesive material, such as polyurethane adhesive, and thereafter the polymeric fibers, such as polyethylene terephthalate (Dacron) fibers, are applied to the adhesive-coated surface so as to adhesively secure the fibers to the surface.
While flocked surfaces formed in the above manner have been found to be effective in implanted devices for encouraging deposition of fibrin from the blood to promote the formation of a viable biological lining and for providing suitable anchoring for such lining, certain problems have been encountered which are attributable to fiber separation and release from the substrate surface into the blood stream, where they are transported to vital organs such as the kidneys and spleen. Investigations have shown that the weakening of the bonds between the polyester fibers and the substrate surface responsible for such release of fibers into the blood stream, is due primarily to the finish which must be applied to the polyester fibers to facilitate handling of the fibers during the flocking operation. Fibers without such finish applied thereto would agglomerate and prevent uniform application of the flock. When the fibers are applied to the adhesive-coated substrate surface, the fiber bonds are, at least partially, between the adhesive and the fiber finish rather than the polyester substrate. Such finish is at least somewhat soluble in water over a long period, and thus is capable of dissolving in contact with blood. If the device is implanted with the fiber finish still remaining on the flocked surface, the finish will be dissolved in vivo and transported to vital organs, such as the lungs, via the blood stream. To minimize the possibility of the finish dissolving in vivo, as much as possible of the fiber finish is preferably removed from the fibers after the flocking operation. In either event, however, the finish removal process, either in vivo or prior to implantation, will result in voids being formed at the spaces initially occupied by the finish. Such voids cause the bonds between the polyester fibers and the substrate surface to be weakened, leading to the fibers becoming separated from the substrate surface and being released into the blood stream.